Story highlights

Kim Jong Nam reportedly fell out of favor with his father over a trip to Tokyo Disneyland

He never met Kim Jong Un because of a practice of raising potential leaders separately

Hong Kong (CNN)The sudden death of North Korean leader Kim Jong Un's half-brother was murder, South Korean officials announced Wednesday.

Kim Jong Nam died Monday soon after becoming ill at Malaysia's Kuala Lumpur International Airport (KLIA) before an outbound flight to Macau.

Lee Cheol Woo, chairman of South Korea's National Assembly Intelligence Committee, told a press briefing Wednesday that Kim had been poisoned, and the suspects were "presumed to be two Asian females."

It's not clear how he obtained that information or how Kim was poisoned.

South Korea's Unification Ministry told CNN they were working with Malaysian authorities to get additional information.

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Many questions still remain around Kim's killing.

Police have described the incident as a "sudden death," pending the results of a postmortem investigation. South Korean media is reporting that Kim was in his 40s.

"So far there are no suspects, but we have started investigations and are looking at a few possibilities to get leads," Selangor State Criminal Investigations Department Chief Fadzil Ahmat told Reuters.

"The deceased ... felt like someone grabbed or held his face from behind," Fadzil said. "He felt dizzy, so he asked for help at the ... counter of KLIA."

South Korea's acting President and Prime Minister held a National Security Council meeting on Wednesday morning to discuss the death, according to a statement released by the Blue House.

Fall from grace

Kim Jong Nam was the most public of all of Kim Jong Il's sons before Kim Jong Un took power, though most remember him for the scandalous headlines he made.

Reports surfaced that Kim Jong Nam fell from favor from the ruling family after he was caught trying to sneak a visit to Tokyo Disneyland using a forged document in 2001 -- an assertion that one journalist who spoke to Kim countered in a 2012 book.

In a picture taken in 2010, Kim Jong Nam, the eldest son of former North Korean leader Kim Jong-Il, waves after an interview with South Korean media representatives in Macau.

It is not clear when he left North Korea, but Kim Jong Nam spent time living in Macau and China and was absent from his father's funeral in 2011, fueling earlier rumors that he had been banished from the country.

Kim was an overweight and careless playboy, but also a smart and open-minded man who was willing to speak out against the family, according to Yoji Gomi, the author of the 2012 book "My Father, Kim Jong Il, and Me."

"He spoke out against his father's 'military first' policy," Gomi told CNN in 2012. "He wants North Korea to embrace economic reform and open its doors."

Kim Jong Nam believed his youngest brother, Kim Jong Un would fail as North Korea's leader, according to Gomi -- though the two brothers never met because of the ancient practice of raising potential successors separately.

A third sibling, Kim Jong Chul, was rumored to have been ruled out as his father's successor for being too "effeminate," Scott Snyder of the Council on Foreign Relations wrote in 2012.

Kim Jong Nam seen arriving at the Beijing International Airport in 2007

Leadership purges

The eldest Kim brother's death comes as Kim Jong Un has purged senior leadership around him, including firing the minister of state security -- one of his top lieutenants -- earlier this month.